When a plural number of substrates such as silicon wafers are heat-treated using, for example, a vertical heat treatment furnace, a substrate support (boat) made of silicon carbide is used. In the substrate support, for example, a supporting groove for supporting a substrate at three points is provided.
In this case, there has been a problem that when the heat treatment is performed at a temperature of about 1000° C. or more, slip dislocation occurs in the substrate near the supporting groove, which may grow into a slip line. When the slip line occurs, flatness of the substrate becomes worse. Therefore, there has been a problem that misalignment of mask (misalignment of mask due to defocusing or deformation) occurs in a lithography process that is one of important processes in a LSI manufacturing process, and thus manufacture of LSI having a desired pattern is difficult.
As means for solving such a problem, a technique is known, wherein first, a dummy wafer is placed in the supporting groove, and then a substrate to be treated is placed on the dummy wafer (refer to patent literature 1). The technique intends that the conventional three-point-support is changed to face-support using the dummy wafer, thereby stress concentration by empty-weight of the substrate to be processed is suppressed and thus warp of the substrate is prevented, and thereby occurrence of the slip dislocation is prevented.
As one of the substrate supports of this type, a boat material such as Si-SiC, on which CVD-SiC coating is formed to prevent impurity contamination from the material, is known (refer to patent literature 2). According to the known example, the CVD-SiC coating is 30 μm to 100 μm in thickness. That is, when the thickness of the coating is less than 30 μm, impurities are diffused from the boat material to a surface of the coating, therefore the object of the CVD coating, or prevention of impurity diffusion by the coating, can not be achieved, and when the thickness of the coating is more than 100 μm, a padding condition that CVD is concentratively deposited onto an edge portion of the boat material occurs, and if the boat (substrate support) is used in this condition, burrs are formed, causing particle contamination.
As another conventional example, a substrate support is known, wherein a SiC film is formed onto a base material such as Si-impregnated sintered-SiC material or graphite by CVD method, so that heat resistance, impact resistance, oxidation resistance, and corrosion resistance are improved (refer to patent literature 3). According to the known example, thickness of the SiC film is preferably 20 μm to 200 μm, and when it is less than 20 μm, since the SiC film itself is damaged, life of the film may be reduced, and when it is more than 200 μm, the SiC film is easily separated.
As still another conventional example, a jig (boat and the like) made of SiC is known, wherein the CVD-SiC coating is applied on a surface of the jig, and a SiO2 film is formed on a surface of the coating (refer to patent literature 4). It is shown from the known example that the SiC coating is for securing uniformity of a surface of the base material, and the thickness of the SiC film is 100 μm, as a practical example. Moreover, it is shown that the SiO2 film is formed for preventing reduction in thickness of the base material in dry cleaning using ClF3, and thickness of the film is desirably 10 Å to 100 μm.
As still another conventional example, it is known that the CVD-SiC is coated about 100 μm on a surface of a support made of Si—SiC (refer to patent literature 5).
[Patent literature 1] JP-A-2000-223495.
[Patent literature 2] JP-A-2000-164522.
[Patent literature 3] JP-A-2002-274983.
[Patent literature 4] JP-A-10-242254.
[Patent literature 5] JP-A-10-321543.